The present invention generally relates to a pressure sensitive element of a small size which is employed as a means for measuring pressure and more particularly, to an optical pressure sensor utilizing Fabry-Perot interference.
Although various kinds of pressure sensitive elements have been developed, since a semiconductor pressure sensor has advantages in that it is small in size and high in accuracy, it has become generally accepted as a means for measuring pressure. The semiconductor pressure sensor has, however, problems in that electrical shielding is necessary in measuring pressure in a human body and noises can to be detected in a strong electromagnetic field because electrical signals are used in measuring pressure. On the other hand, since an optical pressure sensor employing optical signals instead of electric signals does not suffer from the above described problems, pressures can be easily measured. For example, in a type of pressure sensor wherein a diaphragm is mounted on the ends of a bundle of optical fibers so as to detect pressure change as a function of the change of intensity of the reflected light through deflection of the diaphragm, a small pressure sensor which is simple in construction can be obtained with decreased noise. On the contrary, it has a drawback in that the change of the light intensity therein is relatively small. Furthermore, as shown in FIG. 1, a conventional pressure sensor or a sensing portion of a microphone wherein the displacement of the diaphragm is detected by utilizing Fabry-Perot interference, is provided with a diaphragm 5 of a mica sheet or the like having a thickness of 10 .mu.m or more, a fiber 6 on the end surface of which Al is deposited, a spacer 8 of a material such as invar or crystal having a small thermal expansion coefficient and a supporting member 9, while the spacer 8 is fixedly mounted on the supporting member 9 so that the diaphragm 5 and the fiber 6 face each other at a required distance, with an air gap being formed therebetween. However, since the diaphragm 5 and the fiber 6 are caused to adhere closely to the spacer 8, it has been difficult to keep the diaphragm 5 and the fiber 6 in a parallel configuration or to keep the air gap constant in height. Accordingly, because the conventional pressure sensor utilizing Fabry-Perot interference is required to be applied with a machining and assembling process with high accuracy, it has had a problem in that it is limited to small sizes.